1. Technical Field
The present invention relates to a microwave assisted magnetic recording head that adopts a microwave assisted magnetic recording scheme, and a hard-disk drive having the head mounted thereon.
2. Background Art
In recent years, the a real density of HDD (hard-disk drive) has been steadily increasing with the adoption of a perpendicular magnetic recording scheme, and is now about to reach 1 Tb/in2. However, it has become increasingly difficult to write data to magnetic disk media in a smaller track width or bit length and read data from magnetic disk media. In particular, with a reduction in the size of a main pole, which generates a recording magnetic field, of a recording head, the intensity of the recording magnetic field would decrease, so that it would become more difficult to record data on magnetic disk media. Although shingled magnetic recording (SMR) in which overwriting is performed while a wide main pole is gradually shifted by an amount of a track pitch is considered to be used for practical applications, it is not considered that the attainable a real density will increase significantly as the thermal stability of magnetic disk media cannot be improved significantly.
As a technology of recording data on a magnetic disk medium with high thermal stability, i.e., with a high anisotropy field, an energy assisted recording technology is drawing attention. This is a technology of weakening the magnetic field intensity needed for magnetization reversal by applying external energy to a magnetic disk medium, and writing a magnetic signal to the medium on which recording has not been able to be performed with a conventional recording scheme, and achieves both an improvement of the write-ability and a reduction in the size of recording areas. As the energy assisted recording technology, there are known a heat assisted recording technology that performs recording using heat generated by laser irradiation, and a microwave assisted magnetic recording technology that performs recording using a high-frequency magnetic field generated by a high-frequency oscillator.
The microwave assisted magnetic recording technology is a novel technology that has been proposed in recent years, and holds promise in that its built-in assist mechanism of a magnetic head, in particular, is less complicated than that of the heat assisted recording technology. Reference 1 discloses a technology of reducing the intensity of a recording magnetic field by irradiating a magnetic disk medium with a high-frequency magnetic field and thus locally reducing the coercivity of the medium through high-frequency induction heating. Non-Patent Documents 1 and 2 each disclose a technology of recording information on a magnetic disk medium with large magnetic anisotropy by applying a high-frequency magnetic field generated from a field generation layer (FGL), in which magnetization rotates at high speed by using the spin transfer torque effect, provided near a main pole of a perpendicular magnetic head. Further, Patent Document 2 discloses a technology of efficiently recording a positive/negative magnetization state on a magnetic disk medium with large magnetic anisotropy by applying a high-frequency magnetic field while changing the rotation direction in accordance with the polarity of a recording magnetic field, which is generated from a spin torque oscillator with a FGL as one of its components provided between a main pole and a trailing shield of a magnetic recording head.
As disclosed in the above documents, the microwave assisted magnetic recording is actively researched and developed as it can be combined with the conventional perpendicular magnetic recording head and thus is expected to be used for practical applications.